When I add url to the "Configure custom app host", it won't display any UI to the page, it shows only black

I want to test the page on my localhost, and want to sync any changes in plasmic and see the effect in my localhost url as well.

so I tried localhost:3000/plasmic-host and put this url to custom app host configure in plasmic, and it shows all blank.

Actually this is same issue I have in my project :

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